Surprise! Unknown Asteroid Buzzed Earth

[/caption]
A previously undiscovered asteroid came within 14,000 km (8,700 miles) of Earth last week, and astronomers noticed it only 15 hours before closest approach. On Nov. 6 at around 16:30 EST a 7 meter asteroid, now called 2009 VA, came only about 2 Earth radii from impacting our home planet. This is the third-closest known non-impacting Earth approach on record for a cataloged asteroid.
Early on Nov. 6 the asteroid was discovered by the Catalina Sky Survey and was quickly identified by the Minor Planet Center in Cambridge MA as an object that would soon pass very close to the Earth. JPL’s Near-Earth Object Program Office also computed an orbit solution for this object, and determined that it was not headed for an impact.
The two closer approaches include the 1-meter sized asteroid 2008 TS26, which passed within 6,150 km (3,800 miles) of the Earth’s surface on October 9, 2008, and the 7-meter sized asteroid 2004 FU162 that passed within 6,535 km (4,060 miles) on March 31, 2004. On average, objects the size of 2009 VA pass this close about twice per year and impact Earth about once every 5 years.

Only thirteen months ago, another asteroid, 2008 TC3 was discovered under similar circumstances, but that one was found to be on a trajectory headed for the Earth, with impact only about 11 hours away. It impacted in a remote area of Africa; no one was injured and fragments have since been recovered for study.

No word, Jon, on that from NASA yet. I’m sure they’re still figuring out the trajectory of this thing since they’ve just discovered it. If the image they provided is accurate (top), it appears its pass by Earth had a definite effect on the object’s future trajectory.

If you have privy to the ephemeris of the asteroid you can numerically figure this out. The problem is that it might have either gravitationally put the object on an orbit that removes it, or it could be a hunter-chaser resonance that will eventually bring it in.

My hunch is that the asteroid gained some energy from the Earth in the same way that we use planets as gravitational “slingshots” to hurl spacecraft into different orbits. More than likely that would put it out of harms way.

On the other hand there can be resonance conditions set up. The periodicity of close interaction enhances the resonance — BOOM! This is less likely though.

What sort of damage to expect is hard to say. Sufficiently large ones seem to make craters between 7 and 10 times their width. Rocks of a few meters across often break up and do very little damage – like the one which recently came down in Africa. Asteroids of about 30 meters across are supposed to have the potential of being “City Wreckers” – thanks be to Goodness, no proof has been provided…

Early estimates show this object will have an orbital period of about 20 months, and be back at this same spot around Jul 2011. Although, Earth will not be anywhere near this spot at this time.

The orbit seems to take it out past Mars to a distance of approximately 1.94 AU (from the Sun), then comes back in as close as .92 AU (from the Sun), and tilts at about 7 degrees from the ecliptic.
It will swing back out and be at 1 AU in Jan 2010, however it will be out ahead of and below Earth’s orbital plane then.

“This is the third-closest known non-impacting Earth approach on record for a cataloged asteroid.”

“came only about 2 Earth radii from impacting our home planet.”

“On average, objects the size of 2009 VA pass this close about twice per year and impact Earth about once every 5 years.”

So, if this happens every 6 months, and 1 asteroid of this size actually hits the earth every 5 years, isn’t it odd that this is the 3rd closest non-impacting object ever observed?

We must be overestimating the frequency of these impacts or be quite bad at observing near-flying asteroids.

On average, an asteroid of this size passes through the gap between the earths surface and a circle of radius 3 earth radii, so a disc of area 8 pi earth r squared. Yet, only 2 of those have been observed to have been closer in the last 5 1/2 years? A total of 3 of 11 detected?

We don’t use SI mesurements here in America. So, if the article is meant to be read by a US audience, the article should use terms we are familiar with. After all, one wouldn’t write a paper in Japanese if it was meant for an English speaking audience. How hard is it to post US labels as well? Like,